The roll-up curtains are usually rolled up on a roller, which is rotatably carried on a horizontal axis inside a suitable casing situated at top of the window.
The axial rotation of the roller determines rolling and unrolling of the curtain.
According to a known solution, the roll-up curtains are operated manually during both rolling and unrolling.
For this purpose, the head of the roller has a pulley featuring a groove, which engages with an operating chain.
One of the drawbacks of this type of roll-up curtains is the risk of falling during unrolling, i.e. a too quick descent of the curtain can occur due to its weight.
It is to be particularly noted that the falling speed of the curtain increases rapidly during unrolling.
Obviously, this drawback is felt stronger in the special case of relatively heavy curtains.
According to another solution, the roll-up curtains are equipped with a safety device with elastic means situated inside the roller and fastened thereto to facilitate the curtain rolling up.
The curtain unrolling rotation, carried out by acting directly thereon, determines torsion of the elastic means, so that the consequent elastic reaction can be used for rolling up again the curtain.
The elastic means are fastened, at one end, to the roller and at the other end, to a stationary support structure, so that they are stressed in accordance with the curtain unrolling.
To avoid undulations, possible in particular conditions, of the elastic means, these elastic means are fastened at one end to a movable element, which moves axially inside the roller, and are driven into rotation therealong.
For instance, the European Patent EP 0900314 describes improved elastic means, which return a gradual elastic reaction during the curtain rolling up.
The improved elastic means include a plurality of helical springs aimed at rolling the curtain up on a respective roller.
The coil springs are fastened to a common support, keyed to the roller, and to respective support and constraint elements, geometrically fastened to the above roller.
The above described support devices fulfill also the additional task of contrasting the curtain descent, but obviously, they themselves cannot solve the drawback of a curtain possible fall during unrolling.